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NST PRIMARY MIRROR CELL: ANALYSIS AND SOLUTIONS

Explore issues in the primary mirror cell design, resonant frequencies, and proposed improvements for enhanced performance in solar telescopes.

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NST PRIMARY MIRROR CELL: ANALYSIS AND SOLUTIONS

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  1. NST PRIMARY MIRROR CELL:ANALYSIS AND SOLUTIONS Leonid Didkovsky BBSO, 02/11/2004

  2. Do we build a Nondifractionlimited Solar Telescope? Are YOU the author? (Who is responsible?)

  3. Should we be concerned? • Why the PM surface RMS = 21 nm (/15 WF RMS for 632.8 nm) was requested? (See Error budget in LD, JK and PG SPIE 5171-47) • Polishing may be stopped at 41 nm RMS. And What? • Figure on polishing support is worse than 33.5 nm RMS; Astigmatism for model. Higher order in life. Add technology errors. • May it be corrected by PM active system? No. - “Independent” sub-apertures; My estimation is 12/6 Zernike modes; - Moments on PM and the problem with the beam; • By an AO? No in the full 3’ FOV; • What to do: to minimize the polishing errors by re-measuring the mirror and recalculating actuators/forces geometry.

  4. 1. PM Cell Subsystems / Components • Active Primary Mirror • PM Cell Assembly • Axial and Radial Actuators • Load Cells • Thermal sensors • Entrance Aperture • PM Cell Cover • Air Knives and Cooling System BBSO, 02/05/2004

  5. 2. Active Primary Mirror BBSO, 02/05/2004

  6. 3. PM Assembly Picture from Bill Duch’s report BBSO, 02/05/2004

  7. 4. Axial and Radial Actuators BBSO, 02/05/2004

  8. 5. Load Cells Deflection 0.014”/100 lb BBSO, 02/05/2004

  9. 6. Major Requirements • PM Surface Quality on short time scale; • Real-Time control system: WFS and Loads; • Mechanical stability (high resonance freq); • PM Surface Quality on long time scale; • Thermal/Position stability for PM Cell; • Mirror seeing (goal:< 1 deg difference); • Dimensions (thickness < 620 mm); • Weight = 1275 kg (including PM); BBSO, 02/05/2004

  10. 7. Analysis of PM Cell BBSO, 02/05/2004

  11. 7.1. Some static/thermal issues • Connection axial/radial rods to pucks: ± 1 mm tolerance requires about 3 to 6 kg transversal force for radial rod or about 0.6 kg for tangent; • A thermal introduced SE for PM, actuators and Cell is about 3900 nm for 20C cooling. BBSO, 02/05/2004

  12. An Axial (Radial) Rod deformation model 1mm/6kg (short axial) 1mm/0.6 kg (tangent) BBSO, 02/05/2004

  13. Forces map on PM surface for 20C cooling 1 mm tolerance for axial forces will add additional 3-6 kg to shown.

  14. Deflection of the platform (0.4 mm under 560 Kg PM weight).

  15. Deflection of the platform (critical points)

  16. Thermal SE for 20C cooling About 3900 nm PV

  17. 7.2. Resonant Frequencies • For 36 axial supports and ideal (without any deflection) PM Cell: First tone is 44.8 Hz; • PM cell has its first natural tone about 66 Hz; • Combined (Real Cell and PM): First tone is less than 35 Hz, what is lower than the whole telescope requirement: 40 Hz. BBSO, 02/05/2004

  18. 7.2.1. Mirror & Cell 1st tone BBSO, 02/05/2004

  19. 7.2.2. PM & Cell Tip/Tilt 43 Hz BBSO, 02/05/ 2004

  20. 7.2.3. PM & Cell Shifts 56 Hz BBSO, 02/05/2004

  21. 7.2.4. Mirror & Cell 2nd Axial 92Hz BBSO, 02/05/2004

  22. 8. Proposed PM Cell Improvements • Static / Thermal Issues • Special Ball Joints with small backlash; • Resonant Frequencies • Three Hardpoints; • More rigid Platform; • Dimensions (thickness) BBSO, 02/05/2004

  23. 8.1. Ball JointsSpherical plain bearing designs (in USA 1-888-753-2000)http://www.skf.com/portal/skf/home/products/ BBSO, 02/05/2004

  24. An axial actuator

  25. 8.2. Three Hard points Three types of hard points were analyzed: • Three standard axial actuators with 100 lb Load Cell (proposed in “old” design); • Using “harder” Load Cells (1,500 lb instead of 100 lb) at three locations of axial supports; • Using three real hard points (no motion in axial direction). BBSO, 02/05/2004

  26. “Harder” Load Cells: Mode 1,2 (shifts) 56 Hz, 3,4(tip/tilt) 63 Hz, 5 (axial) 69 Hz BBSO, 02/05/2004

  27. Real Hard Points:Modes: 1,2 (shifts) 56 Hz, 3 (torsional) 113 Hz, 4,5 (tip/tilt) 180 Hz, 6 (first axial) 283 Hz BBSO, 02/05/2004

  28. 8.3. More Rigid Platform BBSO, 02/05/2004

  29. Rigid platform eigen mode is 192 Hz compare to 66 Hz in the Old one

  30. 8.4. PM Resonances vs hard points • PM on standard 36 axial supports shows its first axial tone (mode 1) at 44.8 Hz; • PM on three “harder” points shows its first axial tone (mode 5) at 69 Hz; • PM on three hard points shows its first axial tone (mode 6) at 283 Hz. BBSO, 02/05/2004

  31. 8.5. PM & Cell Resonances • PM & Old Cell with 36 Load Cells (100 lb) showed 1st axial tone is less than 35 Hz; • PM & Old Cell with Load Cells (1500 lb) has axial resonant on 40 Hz; • PM & Old Cell with three real hard points has its first axial mode on 47 Hz; • PM & Modified Cell with three hard points showed first axial tone on 135 Hz. BBSO, 02/05/2004

  32. Proposed platform

  33. CONCLUSIONS • Static and dynamical analysis of the Proposed preliminary PM Cell Design showed that some of its assemblies/parts may be improved. • Improved design with three hard points and ribbed platform has axial resonance tone about 135 Hz compare to 35 Hz with “Old” platform and no hard points. BBSO, 02/05/2004

  34. ACKNOWLEDGEMENTS • This work has been supported in part by NASA grant NAG5-12782, NSF grant NSF-ATM-0086999 and AFOSR grant F49620-03-1-0271. • Designing of the PM cell was done by Doug Neill and Bill Duch III. • Analysis, modeling and suggestions for PM Cell improvements were prepared by Mansur Iliyasov and Alexey Zverev (Lavochkin Science-Production Associations, Moscow, Russia). BBSO, 02/05/2004

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